V/Q relationships Breathlessness & Positioning

V/Q relationshipsBreathlessness & Positioning Week 11 Week 11 Tut 1 09-10

Session Plan • Revisit Ventilation / Perfusion definitions and relationships • Positioning for optimising V/Q • Definition of Work of Breathing • Dyspnoea Week 11 Tut 1 09-10

Ventilation Perfusion- Definitions • Alveolar ventilation (V) • Perfusion (Q – from German Quellen meaning to gush) • V/Q matching: ideally = 1 Week 11 Tut 1 09-10

Factors affecting alveolar ventilation • Intrapleural pressure affects ventilation • The more negative it is the less capacity there is for it to become more negative and hence expand the lung • In adults more negative at the apices, less negative at the bases • (Overall more positive in paediatrics) • Lung compliance • Rib cage compliance (paediatrics) • Loading of the diaphragm • Lung pathology • Deviations gas levels in the alveoli • Decrease in O2 causes bronchodilation • Increase in CO2 causes bronchodilation Week 11 Tut 1 09-10

Factors affecting perfusion • Refer to physiology for the factors affecting blood flow to the alveoli such as gravity, transmural pressures • Deviations in the levels of O2 and CO2 in the alveoli • Hypoxaemia causes vasoconstriction • Hypercapnia causes vasoconstriction • SO blood is diverted away from under ventilated alveoli to alveoli that are better ventilated (sometimes confusingly referred to as the blood being shunted away from the under ventilated area) • (NB this is opposite to the systemic circulation) Week 11 Tut 1 09-10

V/Q >1 • More air in the area relative to blood • ↑ dead space • NB physiological versus anatomical dead space • refers to wasted ventilation e.g. • PE • Pulmonary atherosclerosis • Capillary trauma Week 11 Tut 1 09-10

V/Q < 1 • More perfusion than air called a shunt • (NB - shunt can be referred to as anatomical or physiological) • Definition of shunt • Refers to wasted perfusion e.g. • Atelectasis • Consolidation • Tumour occluding main airway Week 11 Tut 1 09-10

Diagnosis of V/Q mismatch • V/Q scan • Usually to rule out a PE • Injection of radioactive particles to view perfusion • Inhalation of inert gases with radioactive tracer • Anterior, Posterior, Right lateral and Left lateral stills taken for ventilation and perfusion and compared • Now being replaced by helical CT scans Week 11 Tut 1 09-10

Normal V/Q Scan Week 11 Tut 1 09-10

Adult pattern of V/Q matching • Meaning of dependent • Ventilation is better in thedependent area of lung – Why? • Perfusion is better in the dependent area of lung – Why? • Which area of lung has the best V/Q match and hence gas exchange? • Which lung has the best V/Q match and hence gas exchange? • The dependent lung Week 11 Tut 1 09-10

Paediatric pattern of V/Q matching • Ventilation preferentially in the non-dependent area of lung – Why? • Perfusion preferentially in the dependent area of lung – Why? • Which lung has the best V/Q matching and hence gas exchange ? • The non- dependent lung • (This pattern is also seen in obese patients) Week 11 Tut 1 09-10

Dyspnoea and WOB • Clinical term for breathlessness reported by the patient: • the sensation of unpleasant or uncomfortable respiration • Results from an increase in the work of breathing • Work of Breathing (WOB) definition • The amount of muscle activity required to overcome the elastic and resistive elements of the respiratory system (Pryor and Prasad, 2008) Week 11 Tut 1 09-10

In small groups what pathophysiological changes may alter the WOB and therefore likely to cause dyspnoea Week 11 Tut 1 09-10

Pathophysiological changes • Increased airways resistance • Decreased lung/chest wall compliance • Weakness of respiratory muscles • Increased metabolic rate • pyrexia • Low cardiac output/ischaemia • Altered ABG’s • Deconditioning • Anaemia • Reduces oxygen carrying capacity of the blood • Other pathologies • e.g. pulmonary oedema Week 11 Tut 1 09-10

Breathlessness/Dyspnoea • In normal healthy individuals breathlessness is a normal response to … • Increased activity • Stress • In small groups think about what happens to your biomechanics of ventilation when you get breathless • For a short period of time (acutely) • Over a long period of time (chronically) Week 11 Tut 1 09-10

Biomechanical changes • Accessory muscle use • upper for inspiration facilitated by fixation of the upper extremities • lower for expiration • Cervical spine extension • open airway and therefore reduce resistance • Shoulder elevation • Due to overuse of the accessory muscles • Audible breaths • open mouth to increase volume of air inspired/decrease airway resistance Week 11 Tut 1 09-10

Prior to Practical • How will positioning impact upon normal V/Q in an adult? • How will positioning impact upon normal V/Q in an infant? • How can positioning be used to assist V/Q matching in a patient with lung pathology and hence optimise oxygenation and removal of carbon dioxide • How can positioning reduce some of the biomechanical changes resulting from sustained breathlessness? Week 11 Tut 1 09-10

Learning Outcomes • describe the relationship of ventilation and perfusion in the healthy adult • describe the relationship of ventilation and perfusion in the healthy child • identify common V/Q mismatches and their signs and symptoms • understand how breathlessness alters biomechanics • begin to understand the theory of positioning in relation to V/Q mismatch • begin to understand the theory of positioning in relation to breathlessness Week 11 Tut 1 09-10

Bibliography • Davies, A. & Moores, C. (2003). The Respiratory System . Edinburgh: Churchill Livingstone • Hough, A. (2001). Physiotherapy in respiratory care. (3rd ed.). Cheltenham, Nelson Thornes. • Pryor, J. A. & Prasad, S. A. (Eds). (2008). Physiotherapy for respiratory and cardiac problems. (4th ed.). Edinburgh: Churchill Livingstone. • Wilkins, R. L., Sheldon, R. L. & Jones Krider, S. (2005). Clinical assessment in respiratory care. (5th ed.). St Louis: Mosby. Week 11 Tut 1 09-10

V/Q relationships Breathlessness & Positioning